Methacrylate and Epoxy Resins Photocured by Means of Visible Light-Emitting Diodes (LEDs)
Traditional curing units emit in a wide wavelength range from UV to IR. Conversely, the spectral output of light-emitting diodes (LEDs) is concentrated in a comparatively narrow wavelength range. In practice, the light absorption of photoinitiators should correlate with the spectral emission profiles of light-curing units compared on an equivalent basis. Only those wavelengths where the photosensitizer absorbs are useful for photopolymerization, the rest of the spectrum is unused and has to be filtered. Since all of the spectral output of the LEDs is absorbed by the photoinitiator, more efficient curing should be possible with current LEDs, resulting in reduced curing time compared with conventional lamps light sources. In addition, it yields the positive aspect of eliminating the IR and UV components. As a result, when compared to conventional curing units, there is less heat transfer to the substrate and no harmful UV rays. In this chapter, the photopolymerization of typical methacrylate and epoxy monomers carried out with LEDs is described.